1. Field of the Invention
The present invention relates to a process for producing a chloromethylated aromatic crosslinked copolymer useful as an intermediate for the production of an anion exchange resin. More particularly, it relates to a method for efficiently recovering chloromethyl methyl ether from a reaction mixture, when a styrene-type crosslinked copolymer is chloromethylated, so that the chloromethylation reaction can be economically carried out.
2. Discussion of Background
An anion exchange resin is produced usually by introducing chloromethyl groups to an aromatic crosslinked copolymer by means of chloromethyl methyl ether and a Lewis acid catalyst, followed by amination with various amines.
In the reaction for introducing chloromethyl groups, it is common to employ an excess amount of chloromethyl methyl ether to accomplish the desired degree of introduction. This excess amount of chloromethyl methyl ether is decomposed with water or an alcohol for treatment after the reaction. Therefore, such a method is not desirable from the economical viewpoint.
On the other hand, as a method for recovering such an excess amount of chloromethyl methyl ether, East German Patents No. 27643 and 113107 disclose a method wherein after a chloromethylation reaction, the chloromethylated polymer is separated by filtration from the reaction solution, and then chloromethyl methyl ether is recovered from the reaction solution. However, chloromethyl methyl ether is a solvent which swells the chloromethylated polymer very well. Accordingly, a substantial amount of chloromethyl methyl ether remains in the chloromethylated polymer thus separated by filtration. In these patents, the chloromethylated polymer separated by filtration, is washed with methanol, whereby the chloromethyl methyl ether remaining in the chloromethylated polymer is decomposed and removed. Such a method is not an efficient recovery method.
Rumanian Patent No. 79140 and Japanese Examined Patent Publication No. 61204/1987 disclose a method wherein concentrated hydrochloric acid, or concentrated hydrochloric acid and formaldehyde as a starting material for chloromethyl methyl ether, are added after completion of a chloromethylation reaction, and then chloromethyl methyl ether is recovered by distillation. By this recovery method, it is possible to recover chloromethyl methyl ether contained in the chloromethylated polymer, and the recovery rate is fairly high. However, when chloromethyl methyl ether is distilled under heating in the presence of concentrated hydrochloric acid, the chloromethyl methyl ether or its decomposition products such as formaldehyde and methanol which are convertible again to chloromethyl methyl ether, will undergo side reactions by the heating to form methyl formate or methyl chloride, thus leading to a recovery loss. Therefore, such a method is not fully satisfactory as a recovery method. A similar recovery method is disclosed also in European Patent No. 0327255.